1. Field of the Invention
The present invention relates to a line driver circuit comprising an emitter follower at the output stage, with the fall time of the output signal of the emitter follower being shortened.
The line driver circuit is used to transmit signals from, for example, a terminal unit, through a transmission line with a length of several tens of meters or several hundred meters, to a computer a long distance away. The output stage of the line driver circuit includes an emitter follower made of transistors. In order to transmit signals over such a long distance, the line driver circuit has to have a large driving capacity. Therefore, the size of the transistors in the emitter follower must be relatively large. The fall time of the output signal of an emitter follower is essentially long in comparison with other transistor logic circuits. When the size of the transistors in the emitter follower is increased, the capacitance between the base and the emitter of each of the respective transistors is also increased and, accordingly, the fall time of the output signal is further elongated, resulting making it difficult to achieve a high-speed operation.
2. Description of the Prior Art
In conventional line driver circuits, there is a diadvantage in that the fall time of the output signal is too long to drive the transmission line at a desired high speed.